1. Field of the Invention
This invention relates to improvements in polyolefin-based plastic composition reinforced with filler and to an automotive molded article such as a molded pillar member for an automotive vehicle, including an interior finish material for covering a pillar or a side roof rail of the automotive vehicle. More particularly, this invention relates to the polyolefin-based plastic composition and an automotive molded pillar member formed of the plastic composition, the plastic composition improving the molded pillar member in flaw resistance upon application of impact load from a sharp cornered part and article.
2. Description of Related Art
In general, a molded article called a garnish is used at the passenger compartment side of an automotive vehicle (particularly, a passenger car) in order to cover a clearance between a ceiling and a door or a clearance between a front windshield glass and a side door glass. This molded article is mainly intended to decorate the upper part of the passenger compartment and used as a design part for covering the above clearance. An example of the garnish (as an interior finish material) is a pillar garnish which is arranged to cover the passenger compartment side of a front pillar formed between a front windshield glass and a side door glass. The front pillar includes an inner panel and an outer panel which are combined at their flange sections by point welding such as spot welding. The interior finish material or pillar garnish is formed of ABS resin or polypropylene resin and includes a main body section which is integrally provided with an installation section formed at the back side surface thereof
The main body section is formed curved to cover the front pillar. The surface of the main body section may be covered with a skin material (not shown) as occasion demands in order to improve design effects. The skin material is a flocked plastic sheet or fabric. The installation section is a clip member which is thrust into a hole or groove in the inner panel of the front pillar, so that the pillar garnish is installed in position. A welt is disposed to cover the clearance between the pillar garnish and the front pillar and a welded section of the inner and outer panels for the purpose of trimming an end section of the pillar garnish at the side which is exposed to the eyes of a vehicle passenger. Additionally, the pillar garnish is provided at its backside surface with reinforcement ribs for the purpose of preventing its opening deformation and providing a stiffness feeling to the pillar garnish.
The pillar garnish is required to have a decorative characteristics, a stiffness feeling and a high quality feeling. Particularly, material of the pillar garnish is required to have a considerable stiffness when installed and upon being heated and to have an excellent moldabiliy which is needed from requirements of design for the pillar garnish. As the material of the pillar garnish, polyolefin-based plastic composition containing filler such as talc has been extensively used to obtain excellent physical properties and moldability.
However, in case that a non-skin pillar garnish is formed of polyolefin-based plastic composition reinforced with filler, the pillar garnish is insufficient in flaw resistance and therefore can be easily flawed and scratched upon collision with a metal part having a sharp corner, such as a tongue of a seat belt. The non-skin pillar garnish is arranged such that, for example, a wrinkle pattern like that of the skin of leather is formed on the surface of the molded article of the plastic composition.
Hitherto, in order to overcome such a defect of the composite material or the polyolefin-based plastic composition containing the filler, the amount of rubber to be blended in the composite material is reduced thereby to increase the stiffness of the molded article or pillar garnish, thus improving the flaw resistance of the pillar garnish. However, with such an improving manner, although the plastic article or pillar garnish exhibits a sufficient flaw resistance against wiping it with a cloth or light interference with the tip end of nail or other automotive parts, a depressed trace is unavoidably left on the surface of the pillar garnish when an impact load is applied from a part having a sharp corner. In fact, under a recent obligation of using a seat belt during driving of the vehicle, a metal part of a buckle and the like of the seat belt will strongly interfere with the pillar garnish when the seat belt is unfasten, increasing problems in which a depressed flaw is left on the surface of the pillar garnish.
In order to overcome such defects of the pillar garnish, it may be proposed that a material (having a high content of rubber) for an automotive bumper is used for the pillar garnish. This improves the flaw resistance of the pillar garnish upon collision of a sharp cornered part or member but lowers the Rockwell hardness and the flexural elastic modulus of the pillar garnish thereby lowering the flaw resistance upon light interference of other part and member and the stiffness of the molded article or pillar garnish. Additionally, a high stiffness material for an automotive bumper has been proposed as disclosed in Japanese Patent Provisional Publication No. 4-56649; however, even the pillar garnish formed of such a material cannot overcome the defect of the Rockwell hardness being insufficient.